1. Field of the Invention
The present invention generally relates to an inductor structure, and more particularly, to an inductor structure having gain leads.
2. Description of Related Art
In general speaking, since an inductor has energy storing and releasing functions, the inductor can be used as an element for stabilizing current. In an integrated circuit (IC), an inductor plays a very important and extreme challenging role and serves as a component, and an inductor is broadly applicable in many fields, such as in radio frequency circuit (RF circuit). In terms of the RF application hereof, an inductor with higher quality means the inductor has a higher quality factor represented by Q-factor, which is defined by:Q=ω×L/R where ω is angular frequency, L is inductance of the inductor coil and R is resistance considering inductance loss under specific frequencies.
There are various methods and techniques today available for incorporating an inductor with IC process. However, in an IC, the limitation of the conductor thickness of an inductor and the interference on an inductor by a silicon substrate would degrade the quality of the inductor. To overcome the problem in the prior art, the conductor loss is reduced by disposing a thicker metal element at the uppermost layer of the inductor so as to advance the Q-factor of inductor. When the above-mentioned metal thickness is increased to a certain degree, the Q-factor improvement becomes not notable.
To overcome the above-mentioned difficulty, in the prior art, a gain lead is employed and disposed under the grounded coil turn, where the gain lead is electrically connected to the coil turn, so as to increase the section area of conductor in the inductor structure which is able to effectively lower conductor loss and advance the quality of the inductor.
Note that although the grounded coil produces an electrical field with a weaker intensity, and the parasitic capacitance caused by the coupling between the gain lead and the substrate of the inductor structure is less; however, the parasitic capacitance does negatively affect the inductance quality of the inductor structure.